Systems and methods for current matching of LED strings

ABSTRACT

System and method are provided for regulating a string current flowing through a string of one or more light emitting diodes. A system controller includes a first controller terminal, a second controller terminal and a third controller terminal. The first controller terminal is coupled to a base terminal of a bipolar junction transistor, the bipolar junction transistor further including an emitter terminal and a collector terminal, the collector terminal being connected to the string of one or more light emitting diodes. The second controller terminal is coupled to the emitter terminal of the bipolar junction transistor and to a first resistor terminal of a resistor associated with a resistance. The third controller terminal is coupled to a second resistor terminal of the resistor. In addition, the system controller is configured to receive a reference voltage, receive an emitter voltage, and output a base current.

1. CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/558,168, filed Jul. 25, 2012, which claims priority to Chinese PatentApplication No. 201210237811.4, filed Jul. 10, 2012, both of theabove-referenced applications being commonly assigned and incorporatedby reference herein for all purposes.

2. BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for currentmatching. Merely by way of example, the invention has been applied tocurrent matching of LED strings. But it would be recognized that theinvention has a much broader range of applicability.

Light emitting diodes (LEDs) have been widely used in variouselectronics products, such as LED/LCD TVs. Often, a LED/LCD TV includesmultiple LED strings. FIG. 1 is a simplified conventional diagramshowing a system for driving multiple strings of LEDs. Each of the LEDstrings 102 ₁, . . . , 102 _(n), where n is no less than 1, has one ormore LEDs connected in series. The system 100 includes bipolar junctiontransistors 104 ₁, . . . , 104 _(n) for driving the LED strings 102 ₁, .. . , 102 _(n) respectively. In addition, the system 100 includes acontroller 108. The emitter terminals 110 ₁, . . . , 110 _(n) of thebipolar junction transistors (BJTs) 104 ₁, . . . , 104 _(n) areconnected to resistors 106 ₁, . . . , 106 _(n), respectively. In orderto match currents 112 ₁, . . . , 112 _(n) flowing through the LEDstrings 102 ₁, . . . , 102 _(n) respectively, voltages at the emitterterminals 110 ₁, . . . , 110 _(n) are often kept equal or approximatelyequal in magnitude. However, conventional techniques often cannot matchthe LED currents with satisfactory accuracy, for example, due to theparameter variations of bipolar junction transistors.

Hence it is highly desirable to improve techniques of current matchingof LED strings.

3. BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for currentmatching. Merely by way of example, the invention has been applied tocurrent matching of LED strings. But it would be recognized that theinvention has a much broader range of applicability.

According to one embodiment, a system controller for regulating a stringcurrent flowing through a string of one or more light emitting diodesincludes a first controller terminal, a second controller terminal, anda third controller terminal. The first controller terminal is coupled toa base terminal of a bipolar junction transistor, the bipolar junctiontransistor further including an emitter terminal and a collectorterminal, the collector terminal being connected to the string of one ormore light emitting diodes. The second controller terminal is coupled tothe emitter terminal of the bipolar junction transistor and to a firstresistor terminal of a resistor associated with a resistance. The thirdcontroller terminal is coupled to a second resistor terminal of theresistor. The system controller is configured to receive a referencevoltage, receive an emitter voltage from the emitter terminal of thebipolar junction transistor through the second controller terminal, andoutput a base current related to the base terminal of the bipolarjunction transistor through the first controller terminal based on atleast information associated with the reference voltage and the emittervoltage. The system controller is further configured to receive a firstcurrent related to the emitter terminal of the bipolar junctiontransistor through the second controller terminal, the first currentbeing equal to the base current in magnitude and regulate the emittervoltage to be equal to the reference voltage in magnitude.

According to another embodiment, a system controller for matching stringcurrents flowing through strings of one or more light emitting diodesincludes a first controller terminal, a second controller terminal, athird controller terminal, a fourth controller terminal, a fifthcontroller terminal and a sixth controller terminal. The firstcontroller terminal is coupled to a first base terminal of a firstbipolar junction transistor, the first bipolar junction transistorfurther including a first emitter terminal and a first collectorterminal, the first collector terminal being connected to a first stringof one or more light emitting diodes. The second controller terminal iscoupled to the first emitter terminal of the first bipolar junctiontransistor and to a first resistor terminal of a first resistorassociated with a first resistance. The third controller terminal iscoupled to a second resistor terminal of the first resistor. The fourthcontroller terminal is coupled to a second base terminal of a secondbipolar junction transistor, the second bipolar junction transistorfurther including a second emitter terminal and a second collectorterminal, the second collector terminal being connected to a secondstring of one or more light emitting diodes. The fifth controllerterminal is coupled to the second emitter terminal of the second bipolarjunction transistor and to a third resistor terminal of a secondresistor associated with a second resistance. In addition, the sixthcontroller terminal is coupled to a fourth resistor terminal of thesecond resistor. The system controller is configured to, receive a firstreference voltage, receive a first emitter voltage from the firstemitter terminal of the first bipolar junction transistor through thesecond controller terminal, and output a first base current related tothe first base terminal of the first bipolar junction transistor throughthe first controller terminal based on at least information associatedwith the first reference voltage and the first emitter voltage. Thesystem controller is further configured to receive a first currentrelated to the first emitter terminal of the first bipolar junctiontransistor through the second controller terminal, the first currentbeing equal to the first base current in magnitude regulate the firstemitter voltage to be equal to the first reference voltage in magnitude.Furthermore, the system controller is configured to, receive a secondreference voltage, receive a second emitter voltage from the secondemitter terminal of the second bipolar junction transistor through thefifth controller terminal, and output a second base current related tothe second base terminal of the second bipolar junction transistorthrough the fourth controller terminal based on at least informationassociated with the second reference voltage and the second emittervoltage. Additionally, the system controller is configured to receive asecond current related to the second emitter terminal of the secondbipolar junction transistor through the fifth controller terminal, thesecond current being equal to the second base current in magnitude andregulate the second emitter voltage to be equal to the second referencevoltage in magnitude. The first reference voltage and the secondreference voltage are the same in magnitude. The first resistance andthe second resistance are the same in magnitude.

In one embodiment, a method for regulating a string current flowingthrough a string of one or more light emitting diodes includes receivinga reference voltage by a system controller including a first controllerterminal, a second controller terminal and a third controller terminal,the first controller terminal being coupled to a base terminal of abipolar junction transistor, the second controller terminal beingcoupled to a first resistor terminal of a resistor associated with aresistance, the third controller terminal being coupled to a secondresistor terminal of the resistor. The method further includes receivingan emitter voltage from an emitter terminal of the bipolar junctiontransistor through the second controller terminal, the bipolar junctiontransistor further including a collector terminal connected to thestring of one or more light emitting diodes. In addition, the methodincludes outputting a base current related to the base terminal of thebipolar junction transistor through the first controller terminal basedon at least information associated with the reference voltage and theemitter voltage, receiving a first current related to the emitterterminal of the bipolar junction transistor through the secondcontroller terminal, the first current being equal to the base currentin magnitude, and regulating the emitter voltage to be equal to thereference voltage in magnitude.

In another embodiment, a method for matching string currents flowingthrough strings of one or more light emitting diodes includes receivinga first reference voltage by a system controller including a firstcontroller terminal, a second controller terminal and a third controllerterminal, the first controller terminal being coupled to a first baseterminal of a first bipolar junction transistor, the second controllerterminal being coupled to a first resistor terminal of a first resistorassociated with a first resistance, a third controller terminal beingcoupled to a second resistor terminal of the first resistor. The methodfurther includes receiving a first emitter voltage from a first emitterterminal of the first bipolar junction transistor through the secondcontroller terminal, the first bipolar junction transistor furtherincluding a first collector terminal connected to a first string of oneor more light emitting diodes. In addition, the method includesoutputting a first base current related to the first base terminal ofthe first bipolar junction transistor through the first controllerterminal based on at least information associated with the firstreference voltage and the first emitter voltage, receiving a firstcurrent related to the first emitter terminal of the first bipolarjunction transistor through the second controller terminal, the firstcurrent being equal to the first base current in magnitude, andregulating the first emitter voltage to be equal to the first referencevoltage in magnitude. Furthermore, the method includes receiving asecond reference voltage by the system controller further including afourth controller terminal, a fifth controller terminal and a sixthcontroller terminal, the fourth controller terminal being coupled to asecond base terminal of a second bipolar junction transistor, the fifthcontroller terminal being coupled to a third resistor terminal of asecond resistor associated with a second resistance, the sixthcontroller terminal being coupled to a fourth resistor terminal of thesecond resistor. Moreover, the method includes receiving a secondemitter voltage from a second emitter terminal of the second bipolarjunction transistor through the fifth controller terminal, the secondbipolar junction transistor further including a second collectorterminal connected to a second string of one or more light emittingdiodes, and outputting a second base current related to the second baseterminal of the second bipolar junction transistor through the fourthcontroller terminal based on at least information associated with thesecond reference voltage and the second emitter voltage. The methodfurther includes receiving a second current related to the secondemitter terminal of the second bipolar junction transistor through thefifth controller terminal, the second current being equal to the secondbase current in magnitude and regulating the second emitter voltage tobe equal to the second reference voltage in magnitude. The firstreference voltage and the second reference voltage are the same inmagnitude. The first resistance and the second resistance are the samein magnitude.

Depending upon embodiment, one or more benefits may be achieved. Thesebenefits and various additional objects, features and advantages of thepresent invention can be fully appreciated with reference to thedetailed description and accompanying drawings that follow.

4. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified conventional diagram showing a system for drivingmultiple strings of LEDs.

FIG. 2 is a simplified diagram showing certain components of a systemfor LED current matching according to an embodiment of the presentinvention.

FIG. 3 is a simplified diagram showing certain components of a systemfor LED current matching according to another embodiment of the presentinvention.

FIG. 4 is a simplified diagram showing a system for driving multiplestrings of LEDs according to an embodiment of the present invention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides systems and methods for currentmatching. Merely by way of example, the invention has been applied tocurrent matching of LED strings. But it would be recognized that theinvention has a much broader range of applicability.

Referring back to FIG. 1, a current flowing through a LED string can bedetermined based on the following equation:

$\begin{matrix}{I_{LED} = {\frac{V_{emitter}}{R} - I_{base}}} & \left( {{Equation}\mspace{14mu} 1} \right)\end{matrix}$where I_(LED) represents a LED current (e.g., the currents 112 ₁, . . ., 112 _(n)), V_(emitter) represents an emitter voltage (e.g., thevoltages at the emitter terminals 110 ₁, . . . , 110 _(n)), R representsa resistance (e.g., resistance of the resistors 106 ₁, . . . , 106_(n)), and I_(base) represents a base current (e.g., base currents 114₁, . . . , 114 _(n) of the BJTs 104 ₁, . . . , 104 _(n) respectively).

As shown in Equation 1, current matching of the LED strings 102 ₁, . . ., 102 _(n) depends on the voltages at the emitter terminals 110 ₁, . . ., 110 _(n), the resistance of the resistors 106 ₁, . . . , 106 _(n), andthe base currents 114 ₁, . . . , 114 _(n). The voltages at the emitterterminals 110 ₁, . . . , 110 _(n) can be matched by generating suchvoltages based on a single reference. The resistance of the resistors106 ₁, . . . , 106 _(n) can often be matched with satisfactory accuracy.However, the base currents 114 ₁, . . . , 114 _(n) usually vary notablyamong different devices. Such mismatch of the base currents 114 ₁, . . ., 114 _(n) may affect the LED current matching accuracy.

FIG. 2 is a simplified diagram showing certain components of a systemfor LED current matching according to an embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The system200 includes a current-matching component 202, a BJT 206, and a resistor208. In addition, the current-matching component 202 includes an erroramplifier 210, and transistors 212, 214, 216, 218 and 220. For example,a collector terminal 227 of the BJT 206 is coupled to a LED string 204.In another example, the error amplifier 210 includes an amplifier 250, atransistor 252 and a current source 254. In yet another example, thecurrent-matching component 202 includes three terminals 280, 282 and284. In yet another example, the BJT 206 is a NPN BJT.

According to one embodiment, the error amplifier 210 receives a feedbacksignal 224 from an emitter terminal 226 of the BJT 206 and a referencesignal 222, and outputs a signal 228 based on the difference between thereference signal 222 and the feedback signal 224 to the transistor 216.For example, a base current 230 (e.g., I_(base)) is generated for theBJT 206 through the terminal 280. In another example, the base current230 is mirrored by at least the transistors 212 and 214 to generate acurrent 232 that flows through the transistor 218. In yet anotherexample, the current 232 is mirrored by at least the transistors 218 and220 to generate a current 234 (e.g., I₁) which flows through thetransistor 220.

According to another embodiment, an emitter current 236 of the BJT 206is determined based on the following equation:I _(emitter) =I _(LED) +I _(base)  (Equation 2)where I_(emitter) represents the emitter current 236, I_(LED) representsa current 238 flowing through the LED string 204 (e.g., a stringcurrent), and I_(base) represents the base current 230. On the otherhand, the emitter current 236 of the BJT 206 can be determined based onthe following equation, for example:I _(emitter) =I _(r) +I ₁  (Equation 3)where I_(emitter) represents a current 240 flowing through the resistor208, and I₁ represents the current 234. Because the current 234 isgenerated based on current mirroring of the base current 230, thecurrent 234 is equal to the base current 230 in magnitude according tocertain embodiments. That is,I ₁ =I _(base)  (Equation 4)

According to Equation 2, Equation 3 and Equation 4, the current 238flowing through the LED string 204 is equal in magnitude to the current240 flowing through the resistor 208, as an example.I_(LED)=I_(r)  (Equation 5)For example, the feedback loop including the error amplifier 210, thetransistor 216 and the BJT 206 is a voltage feedback control loop. Inanother example, the feedback signal 224 is regulated (e.g., set) to beequal or approximately equal in magnitude to the reference signal 222.Thus, the current 240 can be determined as follows, for example:

$\begin{matrix}{I_{r} = \frac{V_{ref}}{R}} & \left( {{Equation}\mspace{14mu} 6} \right)\end{matrix}$where V_(ref) represents the reference signal 222, and R represents theresistance of the resistor 208. In another example, the current 238 canbe determined as follows:

$\begin{matrix}{I_{LED} = \frac{V_{ref}}{R}} & \left( {{Equation}\mspace{14mu} 7} \right)\end{matrix}$Because a current flowing through a single LED string can be determinedusing a reference signal (e.g., the signal 222) and a resistor (e.g.,208) as shown in Equation 7, the currents flowing through the LEDstrings can be matched if a single reference voltage (e.g., thereference signal 222) is received by different error amplifiers (e.g.,the amplifier 210) used for multiple LED strings and resistors (e.g.,the resistor 208) connected to these LED strings in some embodiments.

According to certain embodiments, cascode structures can be used formirroring the base current 230 to generate the current 234 so as toreduce systematic offset for satisfactory current sensing accuracy.However, if the base current 230 has a large magnitude (e.g., 10 mA orlarger), current mirroring using cascode structures may cause headroomissues. Large systematic offset due to channel length modulation mayoccur, which may cause inaccuracy of LED current matching.

FIG. 3 is a simplified diagram showing certain components of a systemfor LED current matching according to another embodiment of the presentinvention. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. The system300 includes a current-matching component 302, a BJT 306, and a resistor308. In addition, the current-matching component 302 includes an erroramplifier 310, amplifiers 344 and 346, and transistors 312, 314, 316,318, 320, 342 and 348. For example, a collector terminal 327 of the BJT306 is coupled to a LED string 304. In another example, the erroramplifier 310 includes an amplifier 350, a transistor 352 and a currentsource 354. In yet another example, the BJT 306 is a NPN BJT.

According to one embodiment, the error amplifier 310 receives a feedbacksignal 324 from an emitter terminal 326 of the BJT 306 and a referencesignal 322, and outputs a signal 328 based on the difference between thereference signal 322 and the feedback signal 324 to the transistor 316.For example, a base current 330 (e.g., I_(base)) is generated for theBJT 306. In another example, the base current 330 is mirrored by atleast the transistors 312 and 314 to generate a current 332 that flowsthrough the transistor 318. In yet another example, the current 332 ismirrored by at least the transistors 318 and 320 to generate a current334 (e.g., I₁) which flows through the transistor 320. In yet anotherexample, the current 334 is equal to the base current 330 in magnitude.In yet another example, the current 338 is equal to the current 340 inmagnitude.

According to another embodiment, the amplifier 344 receives a voltagesignal (e.g., V_(a)) from a terminal 356 of the transistor 314 andanother voltage signal (e.g., V_(b)) from a terminal 358 of thetransistor 312 and outputs a signal 360 to the transistor 342. Forexample, the voltage signal (e.g., V_(a)) at the terminal 356 and thevoltage signal (e.g., V_(b)) at the terminal 358 are kept equal orapproximately equal in magnitude. In another example, the amplifier 346receives a voltage signal (e.g., V_(c)) from a terminal 360 of thetransistor 318 and another voltage signal (e.g., V_(d)) from a terminal362 of the transistor 320 and outputs a signal 362 to the transistor348. In yet another example, the voltage signal (e.g., V_(c)) at theterminal 360 and the voltage signal (e.g., V_(d)) at the terminal 362are kept equal or approximately equal in magnitude. Thus, thetransistors 312 and 314 that are used for current mirroring do not havea systematic offset, and the transistors 318 and 320 that are used forcurrent mirroring do not have a systematic offset according to certainembodiments.

As discussed above and further emphasized here, FIG. 2 and FIG. 3 aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, the BJT 206 is a PNP BJT.The base current 230 flows from the BJT 206 to the terminal 280, and thecurrent 234 flows from the transistor 220 to the terminal 282. Inanother example, the BJT 306 is a PNP BJT. In another example, the basecurrent 330 flows from the BJT 306 to the terminal 380, and the current334 flows from the transistor 320 to the terminal 382.

FIG. 4 is a simplified diagram showing a system for driving multiplestrings of LEDs according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. For example, thesystem 400 includes a controller 401 for driving LED strings 402 ₁, 402₂, . . . , 402 _(i) . . . , 402 _(n), where n is a positive integer(e.g., not smaller than 1) and i is a positive integer no smaller than 1and no larger than n. The system 400 further includes bipolar junctiontransistors (BJTs) 406 ₁, 406 ₂, . . . , 406 _(i) . . . , 406 _(n)connected to the LED strings 402 ₁, 402 ₂, . . . , 402 _(i) . . . , 402_(n) respectively. In another example, the emitter terminals of the BJTs406 ₁, 406 ₂, . . . , 406 _(i) . . . , 406 _(n) are connected toresistors 408 ₁, 408 ₂, . . . , 408 _(i) . . . , 408 _(n), respectively.The controller 401 includes current-matching components 404 ₁, 404 ₂, .. . , 404 _(i) . . . , 404 _(n). For example, the current-matchingcomponent 404 _(i) includes three terminals 410 _(i), 412 _(i) and 414_(i). In another example, the current-matching components 404 ₁, 404 ₂,. . . , 404 _(i) . . . , 404 _(n) are integrated onto a single chip.

In one embodiment, the current-matching component 404 _(i) is the sameas the current-matching component 202. For example, the terminals 410_(i), 412 _(i) and 414 _(i) are the same as the terminals 280, 282 and284 respectively. In another example, the LED string 402 _(i) is thesame as the LED string 204. In yet another example, the BJT 406 _(i) isthe same as the BJT 206. In yet another example, the resistor 408 _(i)is the same as the resistor 208.

In yet another embodiment, the current-matching component 404 _(i) isthe same as the current-matching component 302. For example, theterminals 410 _(i), 412 _(i) and 414 _(i) are the same as the terminals380, 382 and 384 respectively. In another example, the LED string 402_(i) is the same as the LED string 304. In yet another example, the BJT406 _(i) is the same as the BJT 306. In yet another example, theresistor 408 _(i) is the same as the resistor 308.

According to another embodiment, a system controller for regulating astring current flowing through a string of one or more light emittingdiodes includes a first controller terminal, a second controllerterminal, and a third controller terminal. The first controller terminalis coupled to a base terminal of a bipolar junction transistor, thebipolar junction transistor further including an emitter terminal and acollector terminal, the collector terminal being connected to the stringof one or more light emitting diodes. The second controller terminal iscoupled to the emitter terminal of the bipolar junction transistor andto a first resistor terminal of a resistor associated with a resistance.The third controller terminal is coupled to a second resistor terminalof the resistor. The system controller is configured to receive areference voltage, receive an emitter voltage from the emitter terminalof the bipolar junction transistor through the second controllerterminal, and output a base current related to the base terminal of thebipolar junction transistor through the first controller terminal basedon at least information associated with the reference voltage and theemitter voltage. The system controller is further configured to receivea first current related to the emitter terminal of the bipolar junctiontransistor through the second controller terminal, the first currentbeing equal to the base current in magnitude and regulate the emittervoltage to be equal to the reference voltage in magnitude. For example,the system controller is implemented according to at least FIG. 2, FIG.3 and/or FIG. 4.

According to another embodiment, a system controller for matching stringcurrents flowing through strings of one or more light emitting diodesincludes a first controller terminal, a second controller terminal, athird controller terminal, a fourth controller terminal, a fifthcontroller terminal and a sixth controller terminal. The firstcontroller terminal is coupled to a first base terminal of a firstbipolar junction transistor, the first bipolar junction transistorfurther including a first emitter terminal and a first collectorterminal, the first collector terminal being connected to a first stringof one or more light emitting diodes. The second controller terminal iscoupled to the first emitter terminal of the first bipolar junctiontransistor and to a first resistor terminal of a first resistorassociated with a first resistance. The third controller terminal iscoupled to a second resistor terminal of the first resistor. The fourthcontroller terminal is coupled to a second base terminal of a secondbipolar junction transistor, the second bipolar junction transistorfurther including a second emitter terminal and a second collectorterminal, the second collector terminal being connected to a secondstring of one or more light emitting diodes. The fifth controllerterminal is coupled to the second emitter terminal of the second bipolarjunction transistor and to a third resistor terminal of a secondresistor associated with a second resistance. In addition, the sixthcontroller terminal is coupled to a fourth resistor terminal of thesecond resistor. The system controller is configured to, receive a firstreference voltage, receive a first emitter voltage from the firstemitter terminal of the first bipolar junction transistor through thesecond controller terminal, and output a first base current related tothe first base terminal of the first bipolar junction transistor throughthe first controller terminal based on at least information associatedwith the first reference voltage and the first emitter voltage. Thesystem controller is further configured to receive a first currentrelated to the first emitter terminal of the first bipolar junctiontransistor through the second controller terminal, the first currentbeing equal to the first base current in magnitude regulate the firstemitter voltage to be equal to the first reference voltage in magnitude.Furthermore, the system controller is configured to, receive a secondreference voltage, receive a second emitter voltage from the secondemitter terminal of the second bipolar junction transistor through thefifth controller terminal, and output a second base current related tothe second base terminal of the second bipolar junction transistorthrough the fourth controller terminal based on at least informationassociated with the second reference voltage and the second emittervoltage. Additionally, the system controller is configured to receive asecond current related to the second emitter terminal of the secondbipolar junction transistor through the fifth controller terminal, thesecond current being equal to the second base current in magnitude andregulate the second emitter voltage to be equal to the second referencevoltage in magnitude. The first reference voltage and the secondreference voltage are the same in magnitude. The first resistance andthe second resistance are the same in magnitude. For example, the systemcontroller is implemented according to at least FIG. 2, FIG. 3 and/orFIG. 4.

In one embodiment, a method for regulating a string current flowingthrough a string of one or more light emitting diodes includes receivinga reference voltage by a system controller including a first controllerterminal, a second controller terminal and a third controller terminal,the first controller terminal being coupled to a base terminal of abipolar junction transistor, the second controller terminal beingcoupled to a first resistor terminal of a resistor associated with aresistance, the third controller terminal being coupled to a secondresistor terminal of the resistor. The method further includes receivingan emitter voltage from an emitter terminal of the bipolar junctiontransistor through the second controller terminal, the bipolar junctiontransistor further including a collector terminal connected to thestring of one or more light emitting diodes. In addition, the methodincludes outputting a base current related to the base terminal of thebipolar junction transistor through the first controller terminal basedon at least information associated with the reference voltage and theemitter voltage, receiving a first current related to the emitterterminal of the bipolar junction transistor through the secondcontroller terminal, the first current being equal to the base currentin magnitude, and regulating the emitter voltage to be equal to thereference voltage in magnitude. For example, the method is implementedaccording to at least FIG. 2, FIG. 3 and/or FIG. 4.

In another embodiment, a method for matching string currents flowingthrough strings of one or more light emitting diodes includes receivinga first reference voltage by a system controller including a firstcontroller terminal, a second controller terminal and a third controllerterminal, the first controller terminal being coupled to a first baseterminal of a first bipolar junction transistor, the second controllerterminal being coupled to a first resistor terminal of a first resistorassociated with a first resistance, a third controller terminal beingcoupled to a second resistor terminal of the first resistor. The methodfurther includes receiving a first emitter voltage from a first emitterterminal of the first bipolar junction transistor through the secondcontroller terminal, the first bipolar junction transistor furtherincluding a first collector terminal connected to a first string of oneor more light emitting diodes. In addition, the method includesoutputting a first base current related to the first base terminal ofthe first bipolar junction transistor through the first controllerterminal based on at least information associated with the firstreference voltage and the first emitter voltage, receiving a firstcurrent related to the first emitter terminal of the first bipolarjunction transistor through the second controller terminal, the firstcurrent being equal to the first base current in magnitude, andregulating the first emitter voltage to be equal to the first referencevoltage in magnitude. Furthermore, the method includes receiving asecond reference voltage by the system controller further including afourth controller terminal, a fifth controller terminal and a sixthcontroller terminal, the fourth controller terminal being coupled to asecond base terminal of a second bipolar junction transistor, the fifthcontroller terminal being coupled to a third resistor terminal of asecond resistor associated with a second resistance, the sixthcontroller terminal being coupled to a fourth resistor terminal of thesecond resistor. Moreover, the method includes receiving a secondemitter voltage from a second emitter terminal of the second bipolarjunction transistor through the fifth controller terminal, the secondbipolar junction transistor further including a second collectorterminal connected to a second string of one or more light emittingdiodes, and outputting a second base current related to the second baseterminal of the second bipolar junction transistor through the fourthcontroller terminal based on at least information associated with thesecond reference voltage and the second emitter voltage. The methodfurther includes receiving a second current related to the secondemitter terminal of the second bipolar junction transistor through thefifth controller terminal, the second current being equal to the secondbase current in magnitude and regulating the second emitter voltage tobe equal to the second reference voltage in magnitude. The firstreference voltage and the second reference voltage are the same inmagnitude. The first resistance and the second resistance are the samein magnitude. For example, the method is implemented according to atleast FIG. 2, FIG. 3 and/or FIG. 4.

For example, some or all components of various embodiments of thepresent invention each are, individually and/or in combination with atleast another component, implemented using one or more softwarecomponents, one or more hardware components, and/or one or morecombinations of software and hardware components. In another example,some or all components of various embodiments of the present inventioneach are, individually and/or in combination with at least anothercomponent, implemented in one or more circuits, such as one or moreanalog circuits and/or one or more digital circuits. In yet anotherexample, various embodiments and/or examples of the present inventioncan be combined.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

What is claimed is:
 1. A system controller for regulating a stringcurrent flowing through a string of one or more light emitting diodes,the system controller comprising: a first controller terminal coupled toa base terminal of a bipolar junction transistor, the bipolar junctiontransistor further including an emitter terminal and a collectorterminal, the collector terminal being connected to a string of one ormore light emitting diodes; a second controller terminal coupled to theemitter terminal of the bipolar junction transistor and coupled to afirst resistor terminal of a resistor associated with a resistance; anda third controller terminal coupled to a second resistor terminal of theresistor; wherein the system controller is configured to: receive anemitter voltage from the emitter terminal of the bipolar junctiontransistor through the second controller terminal; output a base currentrelated to the base terminal of the bipolar junction transistor throughthe first controller terminal based at least in part on the emittervoltage; and regulate the emitter voltage to be equal to a referencevoltage in magnitude; wherein the system controller further includes: anerror amplifier configured to receive the reference voltage and theemitter voltage and output an amplified signal based at least in part onthe reference voltage and the emitter voltage; a current generatorconfigured to receive the amplified signal and generate the base currentbased at least in part on the amplified signal; and a current mirrorcomponent configured to regulate a first current to be equal to the basecurrent in magnitude, wherein the first current is related to theemitter terminal; wherein the current generator includes a firsttransistor including a first transistor terminal, a second transistorterminal and a third transistor terminal, the first transistor terminalbeing configured to receive the amplified signal, the third transistorterminal being coupled to the first controller terminal and configuredto output the base current; wherein the current-mirror componentincludes: a second transistor including a fourth transistor terminal, afifth transistor terminal and a sixth transistor terminal; a thirdtransistor including a seventh transistor terminal, an eighth transistorterminal and a ninth transistor terminal; a fourth transistor includinga tenth transistor terminal, an eleventh transistor terminal and atwelfth transistor terminal; and a fifth transistor including athirteenth transistor terminal, a fourteenth transistor terminal and afifteenth transistor terminal; wherein: the fourth transistor terminalis coupled to the seventh transistor terminal and the sixth transistorterminal; the fifth transistor terminal is coupled to the eighthtransistor terminal; the sixth transistor terminal is coupled to thesecond transistor terminal; the tenth transistor terminal is coupled tothe thirteenth transistor terminal and the fourteenth transistorterminal; the eleventh transistor terminal is coupled to the secondcontroller terminal and configured to receive the first current; thetwelfth transistor terminal is coupled to the fifteenth transistorterminal; and the fourteenth transistor terminal is coupled to the ninthtransistor terminal.
 2. The system controller of claim 1 is furtherconfigured to regulate the string current to be equal to the referencevoltage divided by the resistance.
 3. The system controller of claim 1is further configured to: output the base current flowing to the baseterminal of the bipolar junction transistor through the first controllerterminal based at least in part on the reference voltage and the emittervoltage; and receive the first current flowing from the emitter terminalof the bipolar junction transistor through the second controllerterminal, the first current being equal to the base current inmagnitude.
 4. The system controller of claim 3 wherein the bipolarjunction transistor is an NPN bipolar junction transistor.
 5. The systemcontroller of claim 1 is further configured to: output the base currentflowing from the base terminal of the bipolar junction transistorthrough the first controller terminal based at least in part on thereference voltage and the emitter voltage; and receive the first currentflowing to the emitter terminal of the bipolar junction transistorthrough the second controller terminal, the first current being equal tothe base current in magnitude.
 6. The system controller of claim 5wherein the bipolar junction transistor is a PNP bipolar junctiontransistor.
 7. A system controller for regulating a string currentflowing through a string of one or more light emitting diodes, thesystem controller comprising: a first controller terminal coupled to abase terminal of a bipolar junction transistor, the bipolar junctiontransistor further including an emitter terminal and a collectorterminal, the collector terminal being connected to a string of one ormore light emitting diodes; a second controller terminal coupled to theemitter terminal of the bipolar junction transistor and coupled to afirst resistor terminal of a resistor associated with a resistance; anda third controller terminal coupled to a second resistor terminal of theresistor; wherein the system controller is configured to: receive anemitter voltage from the emitter terminal of the bipolar junctiontransistor through the second controller terminal; generate a basecurrent related to the base terminal of the bipolar junction transistorthrough the first controller terminal based at least in part on theemitter voltage; and regulate the emitter voltage to be equal to areference voltage in magnitude; wherein the system controller furtherincludes: an error amplifier configured to receive the reference voltageand the emitter voltage and output an amplified signal based at least inpart on the reference voltage and the emitter voltage; a currentgenerator configured to receive the amplified signal and generate thebase current based at least in part on the amplified signal; and acurrent mirror component configured to regulate a first current to beequal to the base current in magnitude, the first current being relatedto the emitter terminal; wherein the current generator includes a firsttransistor including a first transistor terminal, a second transistorterminal and a third transistor terminal, the first transistor terminalbeing configured to receive the amplified signal, the third transistorterminal being coupled to the first controller terminal and configuredto generate the base current; wherein the current-mirror componentincludes: a second transistor including a fourth transistor terminal, afifth transistor terminal and a sixth transistor terminal; a thirdtransistor including a seventh transistor terminal, an eighth transistorterminal and a ninth transistor terminal; a fourth transistor includinga tenth transistor terminal, an eleventh transistor terminal and atwelfth transistor terminal; a fifth transistor including a thirteenthtransistor terminal, a fourteenth transistor terminal and a fifteenthtransistor terminal; a sixth transistor including a sixteenth transistorterminal, a seventeenth transistor terminal and an eighteenth transistorterminal; a seventh transistor including a nineteenth transistorterminal, a twentieth transistor terminal and a twenty-first transistorterminal; a first amplifier including a first amplifier input terminal,a second amplifier input terminal and a first amplifier output terminal;and a second amplifier including a third amplifier input terminal, afourth amplifier input terminal and a second amplifier output terminal;wherein: the fourth transistor terminal is coupled to the seventhtransistor terminal and the sixth transistor terminal; the fifthtransistor terminal is coupled to the eighth transistor terminal; thesixth transistor terminal is coupled to the second transistor terminal;the ninth transistor terminal is coupled to the seventeenth transistorterminal and the first amplifier input terminal; the tenth transistorterminal is coupled to the thirteenth transistor terminal and thefourteenth transistor terminal; the eleventh transistor terminal iscoupled to the twenty-first transistor terminal and the fourth amplifierinput terminal; the twelfth transistor terminal is coupled to thefifteenth transistor terminal; the fourteenth transistor terminal iscoupled to the eighteenth transistor terminal; the sixteenth transistorterminal is coupled to the first amplifier output terminal; thenineteenth transistor terminal is coupled to the second amplifier outputterminal; and the twentieth transistor terminal is coupled to the secondcontroller terminal.
 8. The system controller of claim 7 is furtherconfigured to regulate a string current flowing through the string ofone or more light emitting diodes to be equal to the reference voltagedivided by the resistance.
 9. The system controller of claim 7 isfurther configured to: output the base current flowing to the baseterminal of the bipolar junction transistor through the first controllerterminal based at least in part on the reference voltage and the emittervoltage; and receive the first current flowing from the emitter terminalof the bipolar junction transistor through the second controllerterminal, the first current being equal to the base current inmagnitude.
 10. The system controller of claim 9 wherein the bipolarjunction transistor is an NPN bipolar junction transistor.
 11. Thesystem controller of claim 7 is further configured to: output the basecurrent flowing from the base terminal of the bipolar junctiontransistor through the first controller terminal based at least in parton the reference voltage and the emitter voltage; and receive the firstcurrent flowing to the emitter terminal of the bipolar junctiontransistor through the second controller terminal, the first currentbeing equal to the base current in magnitude.
 12. The system controllerof claim 11 wherein the bipolar junction transistor is a PNP bipolarjunction transistor.